The main active ingredient of marijuana, delta9-tetrahydrocannabinol, acts by binding to selective cell surface receptors called cannabinoid receptors. Activation of these receptors produces intense psychological responses in humans, which suggest that endogenous cannabinoid (endocannabinoid) substances may contribute in important ways to brain functions as diverse as mood, appetite and pain. Several endocannabinoid substances have been identified. Two such substances are anandamide and 2-arachidonoylglycerol (2-AG), lipid-derived compounds that are released from neural cells and activate cannabinoid receptors with high affinity. Anandamide and 2- AG undergo a rapid deactivation process, which contributes to arrest their biological actions. In the case of anandamide, this process is thought to consist of two steps, transport into cells and intracellular hydrolysis by the enzyme fatty-acid amide hydrolase (FAAH). By contrast, much less is known about 2-AG inactivation. In initial studies, we have molecularly cloned rat brain monoacylglycerol lipase (MGL) and provided evidence that this enzyme participates in 2-AG hydrolysis. Based on these results, we propose to test the hypothesis that MGL represents a physiologically relevant route of 2-AG deactivation in the brain. Our first aim is to determine whether hydrolysis by means of MGL contributes to stop the actions of 2-AG at cannabinoid receptors. We will use genetic and pharmacologic manipulations to examine if changes in MGL activity alter the biological disposition of 2-AG by rat brain neurons along with the ability of these cells to respond to 2-AG. Our second aim is to characterize 2-AG transport into neurons and define the role of MGL activity in this process. Our third aim is to combine anatomical and biochemical techniques to elucidate the topographic distribution of MGL in the rat brain. These studies will help reveal the roles played by the endocannabinoid system in the brain and may open innovative avenues for the treatment of neuropsychiatric and substance abuse disorders.